Chapter 9 Formatted InputOutput

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Chapter 9 - Formatted Input/Output
Outline 9.1 Introduction 9.2 Streams 9.3 Format
ting Output with printf 9.4 Printing
Integers 9.5 Printing Floating-Point
Numbers 9.6 Printing Strings and
Characters 9.7 Other Conversion
Specifiers 9.8 Printing with Field Widths and
Precisions 9.9 Using Flags in the printf
Format-Control String 9.10 Printing Literals and
Escape Sequences 9.11 Formatting Input with
scanf
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Objectives

• In this chapter, you will learn
• To understand input and output streams.
• To be able to use all print formatting
  capabilities.
• To be able to use all input formatting
  capabilities.

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9.1 Introduction

• In this chapter
• Presentation of results
• scanf and printf
• Streams (input and output)
• gets, puts, getchar, putchar (in ltstdio.hgt)

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9.2 Streams

• Streams
• Sequences of characters organized into lines
• Each line consists of zero or more characters and
  ends with newline character
• ANSI C must support lines of at least 254
  characters
• Performs all input and output
• Can often be redirected
• Standard input keyboard
• Standard output screen
• Standard error screen
• More in Chapter 11

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9.3 Formatting Output with printf

• printf
• Precise output formatting is accomplished with
  printf
• A printf call contains a format control string
  that describes output format. Format control
  string consists of
• Conversion specifications Conversion specifier
  (), flags, field widths, precisions, and literal
  Characters.
• Can perform rounding, aligning columns,
  right/left justification, inserting literal
  characters, exponential format, hexadecimal
  format, and fixed width and precision
• Format
• printf( format-control-string, other-arguments )
• Format control string describes output format
• Other-arguments correspond to each conversion
  specification in format-control-string
• Each specification begins with a percent sign(),
  ends with conversion specifier

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9.4 Printing Integers
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9.4 Printing Integers

• Integer
• Whole number (no decimal point) 25, 0, -9
• Positive, negative, or zero
• Only minus sign prints by default (later we shall
  change this)

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• fig09_02.c

Program Output

• 455
• 455
• 455
• -455
• 32000
• 2000000000
• 707
• 455
• 4294966841
• 1c7
• 1C7

7x800x817x827x10_7x647448455
7x160Cx1611x1627x112x162567192256455
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9.5 Printing Floating-Point Numbers

• Floating Point Numbers
• Have a decimal point (33.5)
• Exponential notation (computer's version of
  scientific notation)
• 150.3 is 1.503 x 10² in scientific
• 150.3 is 1.503E02 in exponential (E stands for
  exponent)
• use e or E
• f print floating point with at least one digit
  to left of decimal
• g (or G) - prints in f or e with no trailing
  zeros (1.2300 becomes 1.23)
• Use exponential if exponent less than -4, or
  greater than or equal to precision (6 digits by
  default)

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9.5 Printing Floating-Point Numbers
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• fig09_04.c
• Program Output

• 1.234568e006
• 1.234568e006
• -1.234568e006
• 1.234568E006
• 1234567.890000
• 1.23457e006
• 1.23457E006

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9.6 Printing Strings and Characters

• c
• Prints char argument
• Cannot be used to print the first character of a
  string
• s
• Requires a pointer to char as an argument
• Prints characters until NULL ('\0') encountered
• Cannot print a char argument
• Remember
• Single quotes for character constants ('z')
• Double quotes for strings "z" (which actually
  contains two characters, 'z' and '\0')

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• fig09_05.c

A This is a string This is a string This is also
a string
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9.7 Other Conversion Specifiers

• p
• Displays pointer value (address)
• n
• Stores number of characters already output by
  current printf statement
• Takes a pointer to an integer as an argument
• Nothing printed by a n specification
• Every printf call returns a value
• Number of characters output
• Negative number if error occurs
• Prints a percent sign

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9.7 Other Conversion Specifiers
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• fig09_07.c (1 of 2)

Program Output
The value of ptr is 0012FF78 The address of x is
0012FF78   Total characters printed on this line
38   This line has 28 characters 28 characters
were printed   Printing a in a format control
string
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9.8 Printing with Field Widths and Precisions

• Field width
• Size of field in which data is printed
• If width larger than data, default right
  justified
• If field width too small, increases to fit data
• Minus sign uses one character position in field
• Integer width inserted between and conversion
  specifier
• 4d field width of 4

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9.8 Printing with Field Widths and Precisions

• Precision
• Meaning varies depending on data type
• Integers (default 1)
• Minimum number of digits to print
• If data too small, prefixed with zeros
• Floating point
• Number of digits to appear after decimal (e and
  f)
• For g maximum number of significant digits
• Strings
• Maximum number of characters to be written from
  string
• Format
• Use a dot (.) then precision number after
• .3f

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9.8 Printing with Field Widths and Precisions

• Field width and precision
• Can both be specified
• width.precision
• 5.3f
• Negative field width left justified
• Positive field width right justified
• Precision must be positive
• Can use integer expressions to determine field
  width and precision values
• Place an asterisk () in place of the field width
  or precision
• Matched to an int argument in argument list
• Example
• printf( ".f", 7, 2, 98.736 )
• Uses 7 for the field width, 2 for the precision
  and outputs the value 98.74 right justified.

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• fig09_08.c

Program Output

• 1
• 12
• 123
• 1234
• 12345
• -1
• -12
• -123
• -1234
• -12345

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• fig09_09.c

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Using precision for integers 0873
000000873 Using precision for floating-point
numbers 123.945 1.239e002
124 Using precision for strings Happy
Birth

• Program Output

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9.9 Using Flags in the printfFormat-Control
String

• Flags
• Supplement formatting capabilities
• Place flag immediately to the right of percent
  sign
• Several flags may be combined

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• fig09_11.c
• Program Output

hello 7 a 1.230000   hello
7 a 1.230000
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• fig09_12.c
• Program Output

786 -786 786 -786
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• fig09_13.c
• Program Output

547 -547
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• fig09_14.c
• Program Output

02623 0x593 0X593   1427 1427.00
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• fig09_15.c
• Program Output

00000452 000000452
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9.10 Printing Literals and Escape Sequences

• Printing Literals
• Most characters can be printed
• Certain "problem" characters, such as the
  quotation mark "
• Must be represented by escape sequences
• Represented by a backslash \ followed by an
  escape character

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9.10 Printing Literals and Escape Sequences
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scanf

• Important Topics
• Conversion specifiers for scanf Table of Fig
  9.17
• Example Fig 9.18, i d (i can read
  decimal/oct/hex)
• Example Fig 9.19 Floating-point conversion
  specifiers (e/E, g/G, f) scanf using le, lf, lg
  and printing using f
• Example Fig 9.20 Reading char string using c
  s
• Scan set scanf (, z)Example Fig 9.21 A
  set of characters enclosed in , preceded by the
  
• Inverted scan set using caret sign (,
  z) Example Fig 9.22
• Field width Example Fig 9.23
• Assignment suppression character c

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9.11 Formatting Input with scanf
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9.11 Formatting Input with scanf
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9.11 Formatting Input with scanf

• scanf
• Input formatting
• Capabilities
• Input all types of data
• Input specific characters
• Skip specific characters
• Format
• scanf(format-control-string, other-arguments)
• Format-control-string
• Describes formats of inputs
• Other-arguments
• Pointers to variables where input will be stored
• Can include field widths to read a specific
  number of characters from the stream

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9.11 Formatting Input with scanf

• Scan sets
• Set of characters enclosed in square brackets
• Preceded by sign
• Scans input stream, looking only for characters
  in scan set
• Whenever a match occurs, stores character in
  specified array
• Stops scanning once a character not in the scan
  set is found
• Inverted scan sets
• Use a caret aeiou
• Causes characters not in the scan set to be
  stored
• Skipping characters
• Include character to skip in format control
• Or, use (assignment suppression character)
• Skips any type of character without storing it

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• fig09_18.c
• Program Output

Enter seven integers -70 -70 070 0x70 70 70
70 The input displayed as decimal integers
is -70 -70 56 112 56 70 112
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• fig09_19.c

Enter three floating-point numbers 1.27987
1.27987e03 3.38476e-06 Here are the numbers
entered in plain floating-point
notation 1.279870 1279.870000 0.000003
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• fig09_20.c
• Program Output

Enter a string Sunday The input was the
character "S" and the string "unday"
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• fig09_21.c
• Program Output

Enter string ooeeooahah The input was "ooeeooa"
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• fig09_22.c
• Program Output

Enter a string String The input was "Str"
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• fig09_23.c
• Program Output

Enter a six digit integer 123456 The integers
input were 12 and 3456
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• fig09_24.c

Enter a date in the form mm-dd-yyyy
11-18-2003 month 11 day 18 year
2003   Enter a date in the form mm/dd/yyyy
11/18/2003 month 11 day 18 year 2003